In certain power systems, such as winches or screw jacks, the ultimate load device continually exerts a reaction loading force on the driven member; when the drive member ceases delivering drive torque to the driven member, the unopposed reaction force causes the driven member to free wheel backwardly from the position to which it had been moved by the drive member.
The present invention proposes a novel brake means that automatically locks the driven member in any position to which it has been moved by the drive member. In one of its embodiments, the brake means comprises at least one pawl carried by the driven member for interaction with a stationary annular toothed surface. While the drive member is exerting drive torque on the driven member the pawl trips across or around the annular toothed surface; when the drive member ceases delivering drive torque to the driven member, the pawl drops into one of the tooth spaces to lock the driven member against the unopposed free-wheeling reaction forces exerted by the load.
In a preferred two-directional arrangement, two pawls are used. One pawl operates as a locking device to resist clockwise reaction forces; the other pawl resists counterclockwise reaction forces. The drive member has a lost motion connection with the driven member for enabling the driven member to unlock the pawls preparatory to initial force transmission to the driven member.